All organisms need to respond rapidly to new stimuli without being continuously shifted from one behavior to another. An important means of achieving this goal is to induce a stimulus-specific arousal state that is remembered for some time after the stimulus that elicits the arousal is no longer present. The arousal state increases the probability of occurrence of some behaviors and decreases the probability of occurrence of antagonistic behaviors. The long-range goal of the research proposed in this application is to characterize the neural mechanisms that support the persistence of arousal. Specifically we will test a hypothesis that postulates that actions of higher order modulatory neurons are responsible for mnemonic aspects of arousal. We propose to study arousal in the context of ingestive and egestive feeding in Aplysia. We hypothesize that before the state of food-induced arousal is induced, the feeding CPG is in a state that is not dedicated to generating either ingestive or egestive responses. Instead the CPG generates responses that fall along a continuum, i.e., intermediate responses that have both ingestive and egestive characteristics can be generated. As arousal develops we propose that the state of the feeding CPG is altered in a manner that increases the probability of generating ingestive responses and decreases the probability of generating egestive responses. We hypothesize that modulatory serotonergic and peptidergic neurons activate cellular mechanisms that are important for the persistence of such alterations in the state of the CPG. In proposed work we will take a multidisciplinary approach, i.e., we will use electrophysiological, morphological and biochemical techniques to test our hypotheses. Experiments will be conducted in intact, semi-intact and isolated nervous system preparations. When the balance between the need to respond rapidly to new stimuli and the need to persist with one behavior is perturbed, serious behavioral pathologies may emerge (e.g., obsessive compulsive disorders, adult attention deficit disorders, and depression).